The present invention relates generally to a system for removal of chromium ions, in either hexavalent or trivalent form from the waste water of metallic surface treatment solutions, and for the recycling of the treated waste water through subsequent replenishment of the chromium ion content. Specifically, the present invention relates to a process for treatment of the chromium ion containing waste water through passage of the waste water through a settling/clarifying vessel, and withdrawal of the effluent to a holding vessel for gravity passage through active ion exchange resin columns. The process of the present invention permits use of the highly desirable chrome-based seal rinses employed in aqueous pretreatment of metals, without posing ecological dangers.
In the manufacturing industry where painted metallic parts are being produced, pretreatment of metallic surfaces through phosphatizing is extremely common. In conjunction with the phosphatizing, a chrome-based seal rinse operation is highly desirable. Such operations, including spray and dip operations, have been wide-spread in the past, but recent concern with ecological factors has led to attempts to substitute other materials for the chrome-based seal rinse.
Substitutions for the chrome-based seal rinses have not been favorably received. Generally, the surface treatment through exposure to chrome-based seal rinses has provided industry as well as the consumer with a durable corrosion-resistant surface following coating with organic polymeric films. The paint industry, as well as the manufacturing industry have been unable to find acceptable substitutes for the chrome-based seal rinse solutions employed in the past.
While the reasons for the failure of acceptable substitutes are numerous, it has frequently been found that surface adhesion of organic polymeric coatings such as paints has been inferior. Accordingly, it has been found desirable to find alternate systems and/or techniques for disposal of chromate and dichromate containing waste water solutions so that chrome-based solutions may be utilized. Paints and related materials applied to ferrous and nonferrous metals tend to achieve better adhesion and bonding to the substrate which has been treated so as to be slightly acidic, generally in the pH of between about 3.0 and 6.5. Furthermore, freedom from contaminants generally provides more uniform films along with enhanced adhesion.